Platinum complex and organic light-emitting device using the same

ABSTRACT

The present invention relates to a platinum complex as the following formula (I): 
     
       
         
         
             
             
         
       
     
     X n  
         (I)       

     wherein X, n, R 1 , R 2 , R 3 ,R 4 , R 5 , X 1 , X 2 , L 1 , and L 2  are defined the same as the specification. The present invention also further provides an organic light-emitting device using the same. The complexes of the present invention exhibit enhanced emission quantum yields, and short phosphorescence radiative lifetimes in the range of several microseconds so as to be applied in high efficiency OLEDs.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a platinum complex and an organiclight-emitting device using the same and, more particularly, to aphosphorescent platinum complex and a phosphorescent organiclight-emitting device using the same.

2. Description of Related Art

In general, the term “organic light-emitting phenomenon” refers to aphenomenon in which electric energy is converted to light energy bymeans of an organic material. The organic light-emitting device usingthe organic light-emitting phenomenon has a structure usually comprisingan anode, a cathode and organic material layers interposed therebetween.Herein, the organic material layers may be mostly formed in a multilayerstructure comprising layers of different materials, and contain anorganic emissive layer that emits light by fluorescence orphosphorescence. An OLED generally comprises an anode, a hole source, anemissive layer (EML), an electron source and a cathode. The hole sourcemay comprise a hole injection layer (HIL) and a hole transport layer(HTL). The electron source generally comprises an electron transportlayer (ETL) and possibly an electron injection layer (EIL). Some OLEDsalso comprise a thin layer of LiF between the electron source and thecathode. As shown in FIG. 1, there is shown a schematic representationof a typical OLED, comprising a substrate 100 and an anode 101, a holetransport layer 102, a hole injection layer 103, an emissive layer 104,an electron injection layer 105, an electron transport layer 106, a LiFthin layer 107 and a cathode 108 on the surface of the substrate 100 insequence.

The emissive layer (EML), comprised of a host material doped with one ormore luminescent materials, provides the function of light emissionproduced by excitons. The excitons are formed as a result ofrecombination of holes and electrons in the layer.

OLEDs are classified roughly into two types by a difference of mechanismof emission, namely the fluorescent OLED or phosphorescent OLED. It iswell known that the phosphorescent OLED is advantageous from an aspectof emission quantum efficiency.

Owing to their potential to harness the energies of both the singlet andtriplet excitons after charge recombination, transition metal basedphosphorescent materials have recently received considerable attentionin fabricating phosphorescent OLEDs. The main advantages are due to theheavy atom induced singlet-to-triplet intersystem crossing as well asthe large enhancement of radiative decay rate from the resulting tripletmanifolds. In this regard, numerous attempts have been made to exploitthird-row transition metal complexes as dopant emitters for OLEDfabrication, among which quite a few Pt(II), Os(II) and Ir(III)complexes have been reported to exhibit highly efficient deviceperformances. Despite these developments, attempts to further expand thepotential of the square planar Pt(II) complexes, in which the centralmetal ion possesses a higher atomic number than Os(II) and Ir(III) forefficient OLED applications, has encountered many intrinsic obstacles.For example, the PtOEP (H₂OEP=octaethylporphyrin) type of emittercommonly has a ligand based phosphorescence with lifetimes as long as30˜50 μs, so that saturation of emissive sites and a rapid drop indevice efficiency at high drive current is observed. Also contributingto the poor device efficiency is the planar molecular configuration ofmany Pt(II) complexes, which leads to a stacking effect and hence theformation of aggregates or dimers that tend to form excimers in theelectronically excited state.

In addition, as a light source for illumination or backlight, a whitelight is usually required. To realize a white OLED device, plural lightemissive materials such as blue, green, red are used generally. However,blue phosphorescent materials have been the most difficult to prepare.

SUMMARY OF THE INVENTION

The object of the present invention is to reduce the phosphorescenceradiative lifetime and prevent stacking behavior of platinum complexesso as to enhance the potential of platinum complexes for the applicationin high efficiency OLEDs.

To achieve the object, the present invention provides a platinum complexof the following formula (I):

wherein

X is a counter ion;

n is 0 or 1;

X¹ and X² independently are C or N;

R¹, R² and R³ independently are H, C1-C8 alkyl, phenyl, or C1-C4perfluoroalkyl, R¹ is H and R² and R³ together are

or R³ is H and R¹ and R² together are

when X¹ is C;

R¹ and R³ independently are H, C1-C8 alkyl, phenyl, or C1-C4perfluoroalkyl and R² is omitted, when X¹ is N;

R⁴ is H and R⁵ is H, C1-C8 alkyl, phenyl, or C1-C4 perfluoroalkyl, or R⁴and R⁵ together are C4-C8 alkylene or bridged carbocyclic C4-C12alkylene, when X² is C;

R⁴ is omitted and R⁵ is H, C1-C8 alkyl, phenyl, or C1-C4 perfluoroalkyl,when X² is N; and L¹ and L² each are

when n is 1, or together are

when n is 0, wherein X³ is C or N; R⁶ and R⁷ independently are H, C1-C8alkyl, phenyl, or C1-C4 perfluoroalkyl; R⁸ is H, C1-C8 alkyl, phenyl, orC1-C4 perfluoroalkyl; X⁴ and X⁵ independently are C or N; each R′independently is H, C1-C8 alkyl, phenyl, or C1-C4 perfluoroalkyl; X⁶ andX⁷ independently are C or N; R⁹ is H and R¹⁰ is H, C1-C8 alkyl, phenyl,or C1-C4 perfluoroalkyl, or R⁹ and R¹⁰ together are C4-C8 alkylene orbridged carbocyclic C4-C12 alkylene, when X⁶ is C; R⁹ is omitted and R¹⁰is H, C1-C8 alkyl, phenyl, or C1-C4 perfluoroalkyl, when X⁶ is N; R¹¹,R¹² and R¹³ independently are H, C1-C8 alkyl, phenyl, or C1-C4perfluoroalkyl, R¹¹ is H and R¹² and R¹³ together are

or R¹³ is H and R¹¹ and R¹² together are

when X⁷ is C; and R¹¹ and R¹³ independently are H, C1-C8 alkyl, phenyl,or C1-C4 perfluoroalkyl and R¹² is omitted, when X⁷ is N.

In the platinum complex of the formula (I) according to the presentinvention, X can be any free halogen ion, such as chloride ion.

In the platinum complex of the formula (I) according to the presentinvention, preferably, R⁴ is H and R⁵ is H, C1-C8 alkyl, phenyl, orC1-C4 perfluoroalkyl, or R⁴ and R⁵ together are

Herein, R¹⁴, R¹⁵, and R¹⁶ independently are C1-8 alkyl.

In the platinum complex of the formula (I) according to the presentinvention, preferably, R⁹ is H and R¹⁰ is H, C1-C8 alkyl, phenyl, orC1-C4 perfluoroalkyl, or R⁹ and R¹⁰ together are

Herein, R¹⁴, R¹⁵, and R¹⁶ are defined as above.

In the platinum complex of the formula (I) according to the presentinvention, preferably, R¹, R² and R³ independently are H, C1-C8 alkyl,phenyl, or C1-C4 perfluoroalkyl while R⁴ is H and R⁵ is H, C1-C8 alkyl,phenyl, or C1-C4 perfluoroalkyl; or R¹ is H and R² and R³ together are

or R³ is H and R¹ and R² together are

while R⁴ and R⁵ together are

Herein, R¹⁴, R¹⁵, and R¹⁶ are defined as above.

In the platinum complex of the formula (I) according to the presentinvention, preferably, R¹¹, R¹² and R¹³ independently are H, C1-C8alkyl, phenyl, or C1-C4 perfluoroalkyl while R⁹ is H and R¹⁰ is H, C1-C8alkyl, phenyl, or C1-C4 perfluoroalkyl; or R¹¹ is H and R¹² and R¹³together are

or R¹³ is H and R¹¹ and R¹² together are

while R⁹ and R¹⁰ together are

Herein, R¹⁴, R¹⁵, and R¹⁶ are defined as above.

In the platinum complex of the formula (I) according to the presentinvention, more preferably, X¹, X², X³, X⁴, X⁵, X⁶ and X⁷ each are C;R¹, R² and R³ independently are H or C1-8 alkyl, R¹ is H and R² and R³together are

or R³ is H and R¹ and R² together are

R⁴ is H and R⁵ is C1-C4 perfluoroalkyl, or R⁴ and R⁵ together are

R⁶ and R⁷ each are H or C1-C8 alkyl; R⁸ is H or C1-8 alkyl; each R′independently is H or C1-C8 alkyl; R⁹ is H and R¹⁰ is C1-C4perfluoroalkyl, or R⁹ and R¹⁰ together are

R¹¹, R¹² and R¹³ independently are H or C1-8 alkyl, R¹¹ is H and R¹² andR¹³ together are

or R¹³ is H and R¹¹ and R¹² together are

and R¹⁴, R¹⁵ and R¹⁶ are C1-C8 alkyl.

In the platinum complex of the formula (I) according to the presentinvention, the associated ligand chromophores possess a bulky, rigidarchitecture to effectively suppress the aggregation effect.Furthermore, drastic reduction of the phosphorescence radiative lifetimeto several microseconds has been achieved due to the strongsinglet-triplet state mixings.

Specific examples of the platinum complex of the formula (I) accordingto the present invention are shown as follows, but are not limitedthereto.

According to the photophysical measurements, the platinum complexes(I-1) to (I-7) exhibits improved quantum yield and reducedphosphorescence radiative lifetime so as to be applied in a highefficiency OLED. In addition, the platinum complexes (I-3) to (I-7) canemit blue light so as to function as blue phosphorescent materials whichhave been the most difficult to prepare.

Based on the aforementioned properties, the platinum complex of theformula (I) according to the present invention can be employed in anorganic light-emitting device (OLED). The organic light-emitting devicemay be the structure that comprises an anode, a cathode and one or moreorganic material layers including an emissive layer disposed between theelectrodes.

Accordingly, the present invention further provides an organiclight-emitting device, comprising: an anode; a cathode; and one or moreorganic material layers including an emissive layer disposed between theanode and the cathode, wherein at least one layer of the organicmaterial layers comprises the platinum complex of the formula (I).

In the organic light-emitting device of the present invention, theorganic material layers may be formed in a multilayer structurecomprising a hole transport layer (HTL), an emissive layer (EML) and anelectron transport layer (ETL).

In a phosphorescent OLED, a hole blocking layer is often used for theenhancement of luminance efficiency. Thereby, the OLED of the presentinvention can further comprise a hole blocking layer disposed betweenthe electron transport and the emissive layer. In addition, the OLED ofthe present invention also can further comprise a LiF layer between theelectron transport layer and the cathode.

The material of the anode is preferably a material having a large workfunction to facilitate hole injection usually to the organic materiallayers.

The material of the cathode is preferably a material having a small workfunction to facilitate electron injection usually to the organicmaterial layers.

The material of the hole transport layer is a material having high holemobility, which can transfer holes from the anode or the hole injectionlayer toward the emissive layer.

The material of the emissive layer is a material capable of emittingvisible light by accepting and recombining holes from the hole transportlayer and electrons from the electron transport layer, preferably amaterial having high quantum efficiency for fluorescence andphosphorescence.

The material of the electron transport layer is suitably a materialhaving high electron mobility, which can easily receive electrons fromthe cathode and then transfer them to the emissive layer.

In the OLED of the present invention, it is preferable that the emissivelayer comprises a host compound doped with the platinum complex of theformula (I) acting as a guest compound.

The organic light-emitting device according to the present invention maybe of a front-sided, back-sided, or double-sided light emissionaccording to the materials used.

The compound according to the present invention can also function in anorganic electronic device including an organic solar cell, an organicphotoconductor, and an organic transistor, according to a principlesimilar to that applied to the organic light-emitting device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic representation of a typical OLED.

FIG. 2 shows the X-ray structure of Pt(1-iqdzH)Cl₂ synthesized inSynthesis Example 1 according to the present invention.

FIG. 3 shows the X-ray structure of Pt complex (I-2) synthesized inSynthesis Example 2 according to the present invention.

FIG. 4 shows the X-ray structure of Pt complex (I-3) synthesized inSynthesis Example 3 according to the present invention.

FIG. 5 shows the X-ray structure of Pt complex (I-4) synthesized inSynthesis Example 3 according to the present invention.

FIG. 6 shows the X-ray structure of Pt complex (I-7) synthesized inSynthesis Example 5 according to the present invention.

FIG. 7 shows the UV-Vis absorption (in CH₂Cl₂ solution at roomtemperature, -▪-) and emission spectra (in CH₂Cl₂ solution at roomtemperature, -Δ-) of Pt complex (I-1).

FIG. 8 shows the UV-Vis absorption (in CH₂Cl₂ solution at roomtemperature, -□-) and emission spectra (in CH₂Cl₂ solution at roomtemperature, -▴-) of Pt complex (I-2).

FIG. 9 shows the UV-Vis absorption (in CH₂Cl₂ solution at roomtemperature, -▪- for Pt complex (I-3), -◯- for Pt complex (I-4)) andemission spectra (in frozen CH₂Cl₂ matrices at 77K, -★- for Pt complex(I-3), -Δ- for Pt complex (I-4)) of Pt complexes (I-3) and (I-4).

FIG. 10 shows the UV-Vis absorption (in CH₂Cl₂ solution at roomtemperature, -▪- for Pt complex (I-3), -- for Pt complex (I-4)) andemission spectra (in film at room temperature, -□- for Pt complex (I-3),-◯- for Pt complex (I-4)) of Pt complexes (I-3) and (I-4).

FIG. 11 shows the UV-Vis absorption (in CH₂Cl₂ solution at roomtemperature, -▪- for Pt complex (I-5), -◯- for Pt complex (I-6)) andemission spectra (in frozen CH₂Cl₂ matrices at 77K, -★- for Pt complex(I-5), -Δ- for Pt complex (I-6)) of Pt complexes (I-5) and (I-6).

FIG. 12 shows the UV-Vis absorption (in CH₂Cl₂ solution at roomtemperature, -▪- for Pt complex (I-5), -- for Pt complex (I-6)) andemission spectra (in film at room temperature, -□- for Pt complex (I-5),-◯- for Pt complex (I-6)) of Pt complexes (I-5) and (I-6).

FIG. 13 shows the UV-Vis absorption (in CH₂Cl₂ solution at roomtemperature, -▪- for Pt complex (I-5), -- for Pt complex (I-6), -▴- forPt complex (I-7)) and emission spectra (in frozen CH₂Cl₂ matrices at77K, -★- for Pt complex (I-5), -▴- for Pt complex (I-6), -⋆- for Ptcomplex (I-7)) of Pt complexes (I-5), (I-6) and (I-7).

FIG. 14 shows a schematic representation of a phosphorescent OLEDaccording to the present invention.

FIG. 15 shows the current-voltage curves of the organic light-emittingdevices for Pt complex (I-1) at various doping concentrations (-▪- for6%, -- for 12%, -▴- for 24%, -◯- for 50%, -⋆- for 100%).

FIG. 16 shows the emission curves of the organic light-emitting devicesfor Pt complex (I-1) at various doping concentrations (-▪- for 6%, --for 12%, -▴- for 24%, -◯- for 50%, -⋆- for 100%).

FIG. 17 shows the external quantum efficiency-current curves of theorganic light-emitting devices for Pt complex (I-1) at various dopingconcentrations (-▪- for 6%, -- for 12%, -▴- for 24%, -◯- for 50%, -⋆-for 100%).

FIG. 18 shows the luminescence brightness-current curves of the organiclight-emitting devices for Pt complex (I-1) at various dopingconcentrations (-▪- for 6%, -- for 12%, -▴- for 24%, -◯- for 50%, -⋆-for 100%).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, preferable Examples are provided for the purpose of makingthe present invention more understandable. As such, Examples areprovided for illustrating the invention, but the scope of the inventionis not limited thereto.

(A) Synthesis

General procedures: All reactions were performed under nitrogen.Solvents were distilled from appropriate drying agents prior to use.Commercially available reagents were used without further purificationunless otherwise stated. All reactions were monitored by TLC with Merckpre-coated glass plates (0.20 mm with fluorescent indicator UV₂₅₄).Compounds were visualized with UV light irradiation at 254 nm and 365nm. Flash column chromatography was carried out using silica gel fromMerck (230-400 mesh). Mass spectra were obtained on a JEOL SX-102Ainstrument operating in electron impact (EI) or fast atom bombardment(FAB) mode. ¹H and ¹³C NMR spectra were recorded on a Bruker-400 orINOVA-500 instrument; chemical shifts are quoted with respect to theinternal standard tetramethylsilane for ¹H and ¹³C NMR data. Elementalanalysis was carried out with a Heraeus CHN-O Rapid Elementary Analyzer.

X-ray structural analysis: Single crystal X-ray diffraction data weremeasured on a Bruker Smart CCD diffractometer using (Mo-K_(α)) radiation(λ=0.71073 Å). The data collection was executed using the SMART program.Cell refinement and data reduction were made with the SAINT program. Thestructure was determined using the SHELXTL/PC program and refined usingfull-matrix least squares. Non-hydrogen atoms were refinedanisotropically, whereas hydrogen atoms were placed at the calculatedpositions and included in the final stage of refinements with fixedparameters.

SYNTHESIS EXAMPLE 1 Synthesis of Platinum Complex (I-1)

A solution of potassium tetrachloroplatinate (K₂PtCl₄) (200 mg, 0.48mmol),4,8,8-Trimethyl-3-isoquinoline-1-yl-4,5,6,7-tetrahydro-2H-4,7-methano-indazole(1-iqdzH, 146 mg, 0.48 mmol) in H₂O (15 mL) and 4M HCl (1 mL) was heatedto reflux for about 2 hours. After this period, the reaction mixture wascooled and the precipitated solid was filtered off, washed with etherand methanol and dried under vacuum to give Pt(1-iqdzH)Cl₂ as orangesolid (171 mg, 63%).

Spectral data of Pt(1-iqdzH)Cl₂: MS (FAB, ¹⁹⁵Pt): m/z 569 (M)⁺. ¹H NMR(400 MHz, CDCl₃, 298K): δ 11.85 (s, 1H), 9.36 (d, J_(HH)=6.8 Hz, 1H),8.58 (d, J_(HH)=8.4 Hz, 1H), 7.91 (d, J_(HH)=3.6 Hz, 2H), 7.79 (m, 1H),7.64 (d, J_(HH)=6.8 Hz, 1H), 3.46 (d, J_(HH)=3.6 Hz, 1H), 2.34 (m, 1H),2.03 (ddd, J_(HH)=12.3, 9.5, 2.9 Hz 1H), 1.56 (td, J_(HH)=10.7, 3.3 Hz,1H), 1.47 (m, 1H), 1.43 (s, 3H), 1.05 (s, 3H), 0.84(s, 3H). Anal. Calcd.for C₂₀H₂₁Cl₂N₃Pt: C, 42.19; H, 3.72; N, 7.38. Found: C, 42.02; H, 4.03;N, 7.50.

X-ray: Crystals of Pt(1-iqdzH)Cl₂ suitable for X-ray analysis wereobtained by recrystallization from a mixture of dichloromethane andhexane at room temperature.

Selected crystal data of Pt(1-iqdzH)Cl₂: C₂₀H₂₁Cl₂N₃Pt, M=569.39,Triclinic, space group P-1, a=8.1514(1), b=10.0314(2), c=12.0138(2) Å,α=81.8893(9)°, β=85.7748(11)°, γ=83.3597(10)°, V=964.37(3) Å³, Z=2,ρ_(calcd)=1.961 Mgm⁻³, F(000)=548, crystal size=0.25×0.14×0.10 mm³,λ(Mo-K_(α))=0.7107 Å, T=150(2) K, μ=7.561 mm⁻¹, 15484 reflectionscollected (R_(int)=0.0586), final R₁[all data]=0.0356 and wR₂(alldata)=0.0670.

Subsequently, a solution of [Pt(1-iqdzH)Cl₂] (100 mg, 0.18 mmol),picolinic acid (54 mg, 0.44 mmol) and Na₂CO₃ (186 mg, 1.75 mmol) in2-methoxyethanol (30 mL) was heated at 100° C. for 16 hr. An excess ofwater was added after the solution was cooled to room temperature. Theprecipitate was filtered and dried under vacuum. Finally, this mixturewas further purified by silica gel column chromatography (ethyl acetateand hexane=1:1) and recrystallized from CH₂Cl₂ and hexane to give orange[Pt(1-iqdz)(pic)] (compound (I-1), 41 mg, 38%) and red [Pt(1-iqdz)₂] (8mg, 6%).

Spectral data of compound (I-1): MS (FAB, ¹⁹⁵Pt): m/z 620 (M+1)⁺. ¹H NMR(400 MHz, CDCl₃, 298 K): δ 10.50 (d, J_(HH)=6.2 Hz, 1H), 8.73 (m, 2H),8.12 (dd, J_(HH)=8.0, 7.4 Hz, 1H), 8.03 (d, J_(HH)=7.6 Hz 1H), 7.85 (d,J_(HH)=8.0 Hz, 1H), 7.79 (dd, J_(HH)=7.6, 7.2 Hz, 1H), 7.71 (dd,J_(HH)=7.4, 6.2 Hz, 2H), 7.44 (d, J_(HH)=6.8 Hz, 1H), 3.34 (d,J_(HH)=4.0 Hz, 1H), 2.25 (m, 1H), 1.92 (m, 1H), 1.43 (s, 3H), 1.39 (m,2H), 1.02 (s, 3H), 0.81 (s, 3H). Anal. Calcd. for C₂₆H₂₄N₄O₂Pt: C,50.40; H, 3.90; N, 9.04. Found: C, 49.90; H, 4.09; N, 8.75.

SYNTHESIS EXAMPLE 2 Synthesis of Platinum Complex (I-2)

The same procedure was carried out as in Synthesis Example 1 except that3-isoquinoline-3-yl-7,8,8-trimethyl-4,5,6,7-tetrahydro-2H-4,7-methano-indazole(3-iqdzH) was used instead of4,8,8-Trimethyl-3-isoquinoline-1-yl-4,5,6,7-tetrahydro-2H-4,7-methano-indazole(1-iqdzH) and Pt(3-iqdzH)Cl₂ was used instead of Pt(1-iqdzH)Cl₂. Thederivatives [Pt(3-iqdz)(pic)] (compound (I-2)) and [Pt(3-iqdz)₂] can beobtained in 44% and 4% yield.

Spectral data of compound (I-2): MS (FAB, ¹⁹⁵Pt): m/z 620 (M+1)⁺. ¹H NMR(400 MHz, CDCl₃, 298 K): δ 10.51 (d, J_(HH)=5.6 Hz, 1H), 9.55 (s, 1H),8.13 (dd, J_(HH)=8.0, 7.4 Hz, 1H), 8.03 (m, 2H), 7.81 (m, 3H), 7.73 (dd,J_(HH)=7.4, 5.6 Hz, 1H), 7.59 (dd, J_(HH)=8.0, 7.2 Hz, 1H), 3.13 (d,J_(HH)=3.2 Hz, 1H), 2.17 (m, 1H), 1.88 (m, 1H), 1.40 (s, 3H), 1.37 (m,1H), 1.24 (m, 1H), 1.00 (s, 3H), 0.80 (s, 3H). Anal. Calcd. forC₂₆H₂₄N₄O₂Pt: C, 50.40; H, 3.90; N, 9.04. Found: C, 49.95; H, 4.07; N,8.96.

X-ray: Crystals of compound (I-2) suitable for X-ray analysis wereobtained by recrystallization from a mixture of dichloromethane andhexane at room temperature.

Selected crystal data of compound (I-2): C₂₆H₂₄N₄O₂Pt, M=619.58,Monoclinic, space group P2(1), a=10.4558(1), b=19.5010(2), c=10.8625(1)Å, α=90°, β=96.9912(8)°, γ=90°, V=2198.38(4) Å³, Z=4, ρ_(calcd)=1.872Mgm⁻³, F(000)=1208, crystal size=0.25×0.20×0.18 mm³, λ(Mo-K_(α))=0.7107Å, T=150(2) K, μ=6.415 mm⁻¹, 19249 reflections collected(R_(int)=0.0369), final R₁[all data]=0.0277 and wR₂(all data)=0.0647.

SYNTHESIS EXAMPLE 3 Synthesis of Platinum Complexs (I-3) and (I-4)

A solution of potassium tetrachloroplatinate (K₂PtCl₄) (0.21 g, 0.5mmol), 3-trifluoromethyl-5-(2-pyridyl)pyrazole (fppzH, 106 mg, 0.5 mmol)in a mixture of 4 M HCl (1 mL) and water (15 mL) was refluxed for about2 hours. After this period, the reaction mixture was cooled and theprecipitated solid was filtered off, washed with diethyl ether andhexane. Further purification was recrystallization from acetone,affording Pt(fppzH)(Cl)₂ as yellow solid 77% (0.19 g, 0.39 mmol).

Spectral data of Pt(fppzH)(Cl)₂: MS (FAB, ¹⁹⁵Pt): m/z 479 (M⁺), 443(M⁺-HCl). ¹H NMR (400 MHz, d₆-acetone, 298 K): d 9.45 (d, J_(HH)=6.0 Hz,1H), 8.38 (dd, J_(HH)=7.6, 7.2 Hz, 1H), 8.30 (d, J_(HH)=7.6 Hz, 1H),7.88 (s, 1H), 7.77 (dd, J_(HH)=7.2, 6.0 Hz, 1H). ¹⁹F (470 MHz,d₆-acetone, 298 K): δ −61.12 (s, CF₃). Anal. Calcd. for C₉H₆Cl₂F₃N₃Pt:C, 22.56; H, 1.26; N, 8.77. Found: C, 22.37; H, 1.48; N, 8.59.

Subsequently, Pt(fppzH)Cl₂ (0.1 g, 0.21 mmol), pyrazole (36 mg, 0.52mmol) and triethylamine (1 mL) in CH₂Cl₂ was stirred at room temperaturefor about 12 hours. After that, the product mixture was then washed withwater, and concentrated to dryness under reduced pressure, givingpale-yellow powder. Further separation was by silica gel TLC plates(CH₂Cl₂). Trans-[(fppz)Pt(μ-pz)]₂ (compound (I-3)) was recrystallizedfrom CH₂Cl₂ and cis-[(fppz)Pt(μ-pz)]₂ (compound (I-4)) wasrecrystallized from acetone, affording trans-[(fppz)Pt(μ-pz)]₂ as whitesolid 22% (compound (I-3), 0.022 g, 0.023 mmol) andcis-[(fppz)Pt(μ-pz)]₂ as white solid 45% (compound (I-4), 0.045 g, 0.047mmol).

Spectral data of compound (I-3): MS (FAB, ¹⁹⁵Pt): m/z 949 (M⁺). ¹H NMR(400 MHz, d₆-acetone, 298 K): d 8.21 (ddd, J_(HH)=7.6, 7.4, 1.3 Hz, 2H),8.13 (d, J_(HH)=6.0 Hz, 2H), 8.06 (d, J_(HH)=7.4 Hz, 2H), 7.96 (d,J_(HH)=2.4 Hz, 2H), 7.82 (d, J_(HH)=2.0 Hz, 2H), 7.47 (ddd, J_(HH)=7.6,6.0, 1.3 Hz, 2H), 7.20 (s, 2H), 6.48 (dd, J_(HH)=2.4, 2.0 Hz, 2H). ¹⁹F(470 MHz, d₆-acetone, 298 K): δ −60.99 (s, CF₃). Anal. Calcd. forC₂₄H₁₆F₆N₁₀Pt₂: C, 30.39; H, 1.70; N, 14.77. Found: C, 30.27; H, 1.86;N, 14.68.

X-ray: Crystals of compound (I-3) suitable for X-ray analysis wereobtained by recrystallization from dichloromethane at room temperature

Selected crystal data of compound (I-3). CH₂Cl₂: C₂₅H₁₈Cl₂F₆N₁₀Pt₂,M=1033.57, Monoclinic, space group P2(1)/n, a=11.1587(6), b=21.3575(12),c=13.2677(7)Å, α=90°, β=108.591(1)°, γ=90°, V=2997.0(3) Å³, Z=4,π_(calcd)=2.291 Mgm⁻³, F(000)=1928, crystal size=0.16×0.08×0.04 mm³,λ(Mo-K_(α))=0.7107 Å, T=150(2) K, μ=9.578 mm⁻¹, 22499 reflectionscollected (R_(int)=0.0603), final R₁[all data]=0.0557 and wR₂(alldata)=0.0809.

Spectral data of compound (I-4): MS (FAB, ¹⁹⁵Pt): m/z 949 (M⁺). ¹H NMR(400 MHz, d₆-acetone, 298 K): d 8.33 (d, J_(HH)=6.0 Hz, 2H), 8.18 (dd,J_(HH)=7.8, 6.2 Hz, 2H), 8.04 (d, J_(HH)=7.8 Hz, 2H), 7.95 (d,J_(HH)=2.2 Hz, 2H), 7.86 (d, J_(HH)=2.4 Hz, 2H), 7.37 (dd, J_(HH)=6.2,6.0 Hz, 2H), 7.13 (s, 2H), 6.60 (t, J_(HH)=2.2 Hz, 1H), 6.32 (t,J_(HH)=2.4 Hz, 1H). ¹⁹F (470 MHz, d₆-acetone, 298 K): δ −61.16 (s, CF₃).Anal. Calcd. for C₂₄H₁₆F₆N₁₀Pt₂: C, 30.39; H, 1.70; N, 14.77. Found: C,30.22; H, 1.99; N, 14.58.

X-ray: Crystals of compound (I-4) suitable for X-ray analysis wereobtained by recrystallization from acetone at room temperature.

Selected crystal data of compound (I-4). C₃H₆O: C₂₇H₂₂F₆N₁₀OPt₂,M=1006.73, Monoclinic, space group P2(1)/n, a=17.4642(10), b=8.6594(5),c=19.8926(11) Å, α=90°, β=103.6440(10)°, γ=90°, V=2923.5(3) Å³, Z=4,ρ_(calcd)=2.287 Mgm⁻³, F(000)=1888, crystal size=0.25×0.12×0.05 mm³,λ(Mo-K_(α))=0.7107 Å, T=150(2) K, μ=9.641 mm⁻¹, 21992 reflectionscollected (R_(int)=0.0458), final R₁[all data]=0.0457 and wR₂(alldata)=0.0895.

SYNTHESIS EXAMPLE 4 Synthesis of Platinum Complexes (I-5) and (I-6)

Pt(fppzH)(Cl)₂ was prepared by the same procedure as in SynthesisExample 3. Subsequently, Pt(fppzH)Cl₂ (0.1 g, 0.21 mmol),3,5-dimethylpyrazole (dmpzH, 50 mg, 0.52 mmol) and triethylamine (1 mL)in CH₂Cl₂ was stirred at room temperature for about 12 hours. Afterthat, the product mixture was then washed with water, and concentratedto dryness under reduced pressure, giving pale-yellow powder. Furtherseparation was by silica gel TLC plates (CH₂Cl₂).Trans-[(fppz)Pt(μ-dmpz)]₂ (compound (I-5)) was recrystallized fromacetone and cis-[(fppz)Pt(μ-dmpz)]₂ (compound (I-6)) was recrystallizedfrom CH₂Cl₂, affording tran-[(fppz)Pt(μ-dmpz)]₂ as white solid 29%(compound (I-5), 0.03 g, 0.03 mmol) and cis-[(fppz)Pt(μ-dmpz)]₂ as whitesolid 41% (compound (I-6), 0.044 g, 0.044 mmol).

Spectral data of compound (I-5): MS (FAB, ¹⁹⁵Pt): m/z 1004 (M⁺). ¹H NMR(400 MHz, d₆-acetone, 298 K): δ 8.13 (dd, J_(HH)=8.2, 6.8 Hz, 2H), 8.05(d, J_(HH)=6.0 Hz, 2H), 7.95 (d, J_(HH)=8.2 Hz, 2H), 7.39 (dd,J_(HH)=6.8, 6.0 Hz, 2H), 7.06 (s, 2H), 6.00 (s, 2H), 2.42 (s, 6H), 2.32(s, 6H). ¹⁹F (470 MHz, d₆- acetone, 298 K): δ −61.07 (s, CF₃). Anal.Calcd. for C₂₈H₂₄F₆N₁₀Pt₂: C, 33.47; H, 2.41; N, 13.94. Found: C, 33.31;H, 2.58; N, 14.13.

Spectral data of compound (I-6): ¹H NMR (400 MHz, d₆-DMSO, 298 K): δ8.17 (dd, J_(HH)=7.8, 7.0 Hz, 2H), 8.09 (d, J_(HH)=6.2 Hz, 2H), 8.06 (d,J_(HH)=7.8 Hz, 2H), 7.35 (dd, J_(HH)=7.0, 6.2 Hz, 2H), 7.28 (s, 2H),6.19 (s, 1H), 5.91 (s, 1H), 2.27 (br, 12H). ¹⁹F (470 MHz, d₆-DMSO, 298K): δ −59.14 (s, CF₃). Anal. Calcd. for C₂₈H₂₄F₆N₁₀Pt₂: C, 33.47; H,2.41; N. 13.94. Found: C, 33.29; H, 2.61; N, 14.10.

SYNTHESIS EXAMPLE 5 Synthesis of Platinum Complex (I-7)

[Pt(fppzH)Cl₂] was prepared by the same procedure as in SynthesisExample 3. Subsequently, [Pt(fppzH)Cl₂] (150 mg, 0.31 mmol) and3,5-dimethylpyrazole (dmpzH, 75 mg, 0.78 mmol) in 30 mL of CH₂Cl₂ wasstirred at room temperature for 12 hours. After then, the solution waswashed with water and concentrated to dryness under reduced pressure.Further purification was conducted by repeated recrystallization frommethanol solution, from which the less soluble yellow and the relativelymore soluble pale-yellow crystalline solid were identified to be[Pt(fppz)(dmpzH)Cl] (20 mg, 0.04 mmol, 12%) and [Pt(fppz)(dmpzH)₂]Cl(compound (I-7), 100 mg, 0.16 mmol, 52%), respectively.

Spectral data of [Pt(fppz)(dmpzH)Cl]: MS (FAB, ¹⁹⁵Pt): m/z 537 (M−1)⁺.¹H NMR (400 MHz, CD₂Cl₂, 298 K): δ 12.21 (br, 1H), 8.76 (d, J_(HH)=6.5Hz, 1H), 7.75 (t, J_(HH)=7.8, 7.2 Hz, 1H), 7.44 (d, J_(HH)=7.8 Hz, 1H),6.87 (t, J_(HH)=7.2, 6.5 Hz, 1H), 6.84 (s, 1H), 5.94 (br, 1H), 2.41 (s,3H), 2.15 (s, 3H). ¹⁹F NMR (470 MHz, CD₂Cl₂, 298 K): δ −61.32 (s, CF₃).Anal. Calcd. for C₁₄H₁₃ClF₃N₅Pt: C, 31.21; H, 2.43; N, 13.00. Found: C,31.03; H, 2.60; N, 13.10.

Spectral data of compound (I-7): MS (FAB, ¹⁹⁵Pt): m/z 599 (M-Cl)⁺, 598(M-HCl)⁺. ¹H NMR (400 MHz, CD₂Cl₂, 298 K): δ 15.13 (br, 1H), 14.53 (br,1H), 7.97 (m, 1H), 7.74 (d, J_(HH)=7.6 Hz, 1H), 7.08 (m, 2H), 6.90 (s,1H), 6.08 (br, 1H), 6.04 (br, 1H), 2.46 (br, 6H), 2.45 (s, 3H), 2.39 (s,3H). ¹⁹F NMR (470 MHz, CD₂Cl₂, 298 K): δ −61.36 (s, CF₃). Anal. Calcd.for C₁₉H₂₁ClF₃N₇Pt: C,35.94; H, 3.33; N, 15.44. Found: C, 35.77; H,3.60; N, 15.31.

X-ray: Crystals of compound (I-7) suitable for X-ray analysis wereobtained by recrystallization from methanol at room temperature.

Selected crystal data of compound (I-7): Cl₁₉H₂₁ClF₃N₇Pt, M=634.97,Monoclinic, space group P2(1)/c, a=10.9312(10), b=20.0897(19),c=9.9253(10) Å, α=90°, β=98.352(2)°, γ=90°, V=2156.5(4) Å³, Z=4,ρ_(calcd)=1.956 Mgm⁻³, F(000)=1224, crystal size=0.42×0.30×0.05 mm³,λ(Mo-K_(α))=0.7107 Å, T=150(2) K, μ=6.678 mm⁻¹, 16284 reflectionscollected (R_(int)=0.0594), final R₁[all data]=0.0344 and wR₂(alldata)=0.0771.

(B) Spectroscopic and Dynamic Measurement

Steady-state absorption and emission spectra were recorded on a Hitachi(U-3310) spectrophotometer and an Edinburgh (FS920) fluorimeter,respectively. Both wavelength-dependent excitation and emission responseof the fluorimeter were calibrated. A configuration of front-faceexcitation was used to measure the emission of the solid sample, inwhich the cell was made by assembling two edge-polished quartz plateswith various Teflon spacers. A combination of appropriate filters wasused to avoid interference from the scattering light. Lifetime studieswere performed by an Edinburgh FL 900 photon-counting system with ahydrogen-filled/or a nitrogen lamp as the excitation source. Data wereanalyzed using a nonlinear least squares procedure in combination withan iterative convolution method. The emission decays were analyzed bythe sum of exponential functions, which allows partial removal of theinstrument time broadening and consequently renders a temporalresolution of ˜200 ps.

To determine the photoluminescence quantum yield in solution, sampleswere degassed by three freeze-pump-thaw cycles under vigorous stirringconditions. 4-(Dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM, λem=615 nm, Exciton, Inc.) in methanol was usedas a reference, assuming a quantum yield of 0.43 with a 430 nmexcitation. An integrating sphere (Labsphere) was applied to measure thequantum yield in the solid state, in which the solid sample film wasprepared via direct vacuum deposition methods. The resultingluminescence was led to an intensified charge-coupled detector forsubsequent quantum yield analyses. To obtain the PL quantum yield insolid state, the emission was collected via integrating sphere, and thequantum yield was calculated according to a reported method. [J. C. deMello, H. F. Wittmann, R. H. Friend, Adv. Mater. 1997, 9, 230.]

The photophysical properties of platinum complexes (I-1) to (I-7) areshown in Table 1. The absorption spectra and the emission spectrathereof are shown in FIGS. 7-13.

TABLE 1 λ_(max(absorption)) (ε × 10³, λ_(max(emission)) Φ τ_(obs) k_(r)k_(nr) Complex M⁻¹cm⁻¹) (nm) (%) (μs) (s⁻¹) (s⁻¹) I-1 329(7.7), 587, 61264 8.2 7.8 × 10⁴ 4.4 × 10⁴ 345(11.1), 372(8.7), 388(9.2), 450(2.5) I-2326(23.0), 567   3.5 0.85 4.1 × 10⁴ 1.1 × 10⁶ 376(6.4), 434(2.0) I-3263(25.9), (446, 476, 502); (55) (9.1); (6.0 × 10⁴) (5.0 × 10⁴)316(22.4), [445, 470, 500, 540] [20.9] 355(5.1) I-4 266(27.0), (451,478, 506); (28) (6.1); (4.6 × 10⁴) (1.2 × 10⁵) 318(23.9), [440, 472,500, 540] [20.8] 349(7.5) I-5 262(25.0), (450, 476, 502); (56) (4.5);(1.2 × 10⁵) (9.7 × 10⁴) 322(12.3), [441, 471, 496, 535] [20.6] 341(8.0)I-6 273(18.2), (453, 479, 506) (13) (0.53); (2.4 × 10⁵) (1.6 × 10⁶)317(13.4), [445, 476, 501, 538] [18.9] 343(7.4) I-7 311(9.6), (447, 474,498) (38) (7.4); (5.1 × 10⁴) (8.4 × 10⁴) 342(3.2) [440, 468, 496, 534][42.8]

In Table 1, k_(r) and k_(nr) were calculated according to the equations,k_(r)=Φ/τ_(obs) and k_(nr)=(1/τobs)−k_(r); absorption data were recordedin CH₂Cl₂ solution; and PL data measured in solid film at RT and inCH₂Cl₂ matrix at 77K are depicted in parentheses and square bracket,respectively. (Unless Complexes I-1 and I-2 were recorded in CH₂Cl₂solution)

The absorption and luminescence spectra recorded for platinum complexes(I-1) and (I-2) in CH₂Cl₂ are depicted in FIGS. 7 and 8, while pertinentdata are listed in Table 1. Several remarks can be pointed out from thecorresponding spectroscopic and dynamic measurements. As shown in theabsorption spectra, the first transition band for the platinum complexes(I-1) and (I-2) were located at ˜450 nm and 434 nm, respectively. Theresults can be rationalized by the S₀→S₁ transition for the platinumcomplexes (I-1) and (I-2) being mainly ascribed to the metal-to-ligandcharge transfer transition (MLCT) mixed with the intra-ligand chargetransfer transition (ILCT) from indazole to isoquinoline moieties,namely 1-iqdz for the platinum complex (I-1) and 3-iqdz for the platinumcomplex (I-2), respectively.

In addition, the S₀→S₁ transition for the platinum complex (I-1) tendsto be red shifted with respect to that of the platinum complex (I-2)under the same iqdz ligands. For example, the S₀→S₁ peak wavelength forthe platinum complex (I-1) of 450 nm is bathochromic shift by 16 nmcompared to the platinum complex (I-2) of 434 nm (see Table 1). Theresult can be tentatively rationalized by the more facile π-electrondelocalization in the case of 1-iqdz (the platinum complex (I-1)),lowering the π* energy and hence a smaller energy gap of the mixedMLCT(d_(π)→π*)/ILCT(π→π*) transition.

As for the emission shown in FIGS. 7 and 8, for the platinum complexes(I-1) and (I-2) studied, the origin of phosphorescence is unambiguousdue to its significant O₂ quenching as well as the rather long emissionlifetime of microseconds (see Table 1). In a good correlation with thetrend of absorption spectra, the emission peak wavelength of theplatinum complex (I-1) revealed red shift with respect to that of theplatinum complex (I-2) bearing the same iqdz ligands (see FIGS. 7-8 andTable 1). More interestingly, in the room temperature, degassed CH₂Cl₂solution, the platinum complex (I-1) exhibit more intense emission yieldas compared to that of the platinum complex (I-2). With emission quantumyield and observed lifetime provided, both radiative and nonradiativedecay rates can be deduced and the values are listed in Table 1. Whilethe deduced radiative decay rates, k_(nr) for the platinum complex (I-2)(1.1×10⁶ s⁻¹ , see Table 1) is larger than that of the platinum complex(I-1) (4.4×10⁴ s⁻¹ ) by 25 folds. An equally interesting remark is inthat the radiative decay rate for the platinum complex (I-1) iscalculated to be larger than that for the platinum complex (I-2) bynearly 2 fold. In comparison to the platinum complex (I-2), the increase(decrease) of the radiative (nonradiative) decay rate leads to asignificant increase of the emission quantum efficiency for the platinumcomplex (I-1).

Theoretically, the larger radiative decay rate corresponds to moreallowed S₀-T₁ transition. Based on the first order approximation, italso implies the enhancement of spin-orbit coupling integral, mostlikely from the more d_(π)contribution of the core heavy metal atomPt(II). In other words, comparing with the platinum complex (I-2), theexperimental results render a proposal of more MLCT contribution for theplatinum complex (I-1) in the T₁ manifold.

As the platinum complexes (I-1) and (I-2), the dinuclearpyrazolate-bridge complexes (I-3) to (I-6) and the mononuclear complex(I-7) also exhibit enhanced emission quantum yields and shortphosphorescence radiative lifetimes in the range of severalmicroseconds, resulting from the steric hinderance preventing stackingbehavior of the platinum complexes. In addition, the platinum complexes(I-3) to (I-7) bear fppz ligands leading blue emission.

As for the absorption shown in FIGS. 9 to 12, for the platinum complexes(I-3) to (I-6) studied, the high energy absorption bands at ˜320 nm ofthe platinum complexes (I-3) to (I-6) can be reasonably assigned to theazolate→pyridine intra-ligand ππ* transition, which is also identifiedby their large extinction coefficients of 1.2˜2.4×10⁴ M⁻¹ cm⁻¹ . Thenext lower energy band with the peak wavelength at ˜350 nm is assignedto the spin allowed ¹MLCT transition due to its relatively lowerextinction coefficient of <7×10³ M⁻¹ cm⁻¹.

Moreover, in comparison to the mononuclear complex (I-7) (see FIG. 13),the lower lying absorption of dinuclear complexes (I-5) (or complexes(I-6)) is slightly red-shifted in peak wavelength and the associatedextinction coefficient is approximately twice larger. These resultssuggested that the electronic transitions character of dinuclearcomplexes (I-5) (or complexes (I-6)) can be qualitatively divided intotwo structural segments resemble that of (I-7), and the Pt—Ptinteraction in the dinuclear complexes should be responsible for theobserved small difference in energy gaps.

We unfortunately could not resolve any emission for all isomericplatinum complexes of (I-3) to (I-6) in the degassed CH₂Cl₂ solution atroom temperature. Taking account of the sensitivity of current detectingsystem, the emission yield, if there is any, is concluded to be lessthan 10 ⁻⁴. Such an observation is similar to many Pt(II) complexeswhich are emissive in the solid state at RT and as glassy solution atlower temperature, whereas they are totally non-emissive in fluidsolutions at RT. Perhaps, the quenching processes associated with e.g.solvent collision and/or large amplitude motions can be drasticallyreduced by freezing solvent molecules in the cryogenic temperature or ina form of solid film. Evidence of this is provided by the strongemission acquired in the 77 K CH₂Cl₂ matrix as well as in the roomtemperature solid film for both platinum complexes (I-3) to (I-6) (seeFIGS. 9 to 12). In solid film, the deduced radiative lifetime of <25 μsfor all isomers ensures the origin of emission from the tripletmanifold, i.e. the phosphorescence. The short radiative lifetime, incombination with the feature of vibronic progression in emissionspectra, manifests the T₁-S₀ transition to be with ligand ππ* propertiesmixed, in part, with the metal-to-ligand charge transfer character.

One remarkable feature revealed in FIGS. 9 to 12 lies in the emissionspectral similarity between solid film and 77 K CH₂Cl₂ matrix in termsof peak wavelength and vibronic progression, except the changes ofintensity ratio among the vibronic peaks. Upon quickly plunging thesample (being diluted in CH₂Cl₂) into the liquid nitrogen environment,the platnium complexes (I-3) to (I-6) should exist in a well dispersed,monomeric form. It is thus reasonable to conclude negligibleintermolecular Pt—Pt interaction for the platinum complexes (I-3) to(I-6). Knowing such interaction frequently takes place in Pt(II)complexes, the negligible Pt(II) packing interaction in solid film forthe platinum complexes (I-3) to (I-6) can be rationalized by the overallnonplanar structure, in which two Pt(II) units are spatially twistedwith respect to each other, avoiding the intermolecular interaction. Ina good correlation with the absorption spectra, the phosphorescence peakof the platinum complex (I-3) (λ_(max)=476 nm) and (I-5) (λ_(max)=476nm) in solid film is slightly blue shifted with respect to that of (I-4)(λ_(max)=478 nm) and (I-6) (λ_(max)=479 nm). Furthermore, the platinumcomplexes (I-3) and (I-5) (complex (I-3): Φ=0.55, complex (I-5): Φ=0.56)are in higher emission quantum yield than the platinum complexes (I-4)and (I-6) (complex (I-4): Φ=0.28, complex (I-6): Φ=0.13). The higheremission quantum yield in the platinum complexes (I-3) and (I-5) ismainly due to their smaller nonradiative decay rate, k_(nr). Forexample, k_(nr) was deduced to be 1.6×10⁶ s⁻¹ for the platinum complexe(I-6), which is larger than that (9.7×10⁴ s⁻¹) for the platinum complexe(I-5) by one order of magnitude.

Accordingly, the present invention provides the complexes (I-1) and(I-2) exhibiting enhanced potential for the application in highefficiency orange OLEDs, and the complexes (I-3) to (I-6) exhibitingenhanced potential for the application in high efficiency blue OLEDswhich have been the most difficult to prepare.

(C) OLED Fabrication

Charge transporting materials such as NPB{4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl} and Alq₃[tris(8-hydroxyquinolinato)aluminum (III)], as well as the host materialCBP (4,4′-N.N′-dicarbazolyl-1,1′-biphenyl) were synthesized according toliterature procedures, [A. Y Sonsale, S. Gopinathan, C. Gopinathan,Indian J Chem. 1976, 14, 408; B. E. Koene, D. E. Loy, M. E. Thompson,Chem. Mater. 1998, 10, 2235] and were sublimed twice through atemperature-gradient sublimation system before use. BCP(2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline) was obtained fromAldrich. Patterned ITO-coated glass substrates (sheet resistance ≦30ohms/square) with an effective individual device area of 3.14 mm² werecleaned by sonication in a detergent solution, water and ethanol,respectively and then dried by a flow of nitrogen. The substrates werefurther treated with oxygen plasma for 3 min before loading into thevacuum chamber. Various organic layers were deposited sequentially at arate of 0.1˜0.3 nm/s under a pressure of 2×10⁻⁵ Torr in an UlvacCryogenic deposition system. Phosphorescent dopants were co-evaporatedwith CBP via two independent sources. A thin layer of LiF (1 nm) and athick layer of Al (150 nm) were followed as the cathode.

DEVICE EXAMPLE 1

Anode: Indium tin oxide (ITO);

Hole transport layer (HTL, 40 nm):4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB);

Emissive layer (EML, 30 nm): carbazole biphenyl (CBP) doped with Complex(I-1), with dopant concentration of 6%, 12%, 24%, 50% and 100%;

Hole blocking layer (10 Onm): bathocuproine (BCP);

Electron transport layer (ETL, 30 nm): tris(8-hydroxyquinolinato)aluminium (III) (Alq₃);

Cathode: Al (150 nm)/LiF layer (1 nm).

The schematic representation of a phosphorescent organic light-emittingdevice of the present invention is shown in FIG. 14. The phosphorescentorganic light-emitting device of the present invention comprises asubstrate 200 and an anode 201, a hole transport layer 202, an emissivelayer 203, a hole blocking layer 204, an electron transport layer 205, aLiF thin layer 206 and a cathode 207 on the surface of the substrate 200in sequence.

The crucial device performance characteristics are collected in Table 2,showing the systematic trend that varied according to the five dopantconcentrations from 6% to 100%. Orange emission was observed for all theconcentrations applied, while the one with a pure layer of the Pt(II)emitter showed the lowest brightness and device efficiencies. FIG. 15depicts the current-voltage curves of the organic light-emitting devicesfor Pt complex (I-1) at various doping concentrations, for which thedevice with 12% of Pt complex (I-1) showed the highest current densitycompared with all other devices operated under identical voltages.Concomitantly, a small red shifting of the EL emission was observed withincreasing dopant concentrations, e.g. from λ_(max)=581 nm for the 6%device to 618 nm for the device with neat dopant (FIG. 16). Thisred-shifting effect is presumably attributed to the occurrence ofcertain degree of intermolecular ππ stacking interaction with increasingthe concentration of the planar Pt(II) complex.

Moreover, among varying the dopant concentrations, the best deviceperformance was achieved at 6 wt % (FIG. 17), which rendered a turn-onvoltage of 3 V (at 1 cd/m²) and maximum EQE (external quantumefficiency) of 5.78 at 5 V, gave CIE coordinates of (0.57, 0.43) at 8 V,and reached the maximum brightness of 20296 cd/m² at a driving voltageof 16 V. Like other phosphorescent OLED devices, their efficiencies alsowitnessed a significantly drop with increasing driving voltage. This canbe confirmed by the observation that, at a driving current of 20 mAcm⁻², the external quantum efficiency and luminous efficiency are 4.93%and 12.19 cd A⁻¹, while the efficiencies reduced to 3.16% and 7.82 cdA⁻¹ at 100 mA cm⁻², respectively.

Finally, as a result of concentration quenching, raising the dopingconcentration led to a drastic falloff in device efficiencies.Relatively bright luminescence was also observed for other concentrationapplied, despite a significant decrease of intensity once theconcentration was increased over 6% (FIG. 18), the result of which wasevidenced by making a device using 12% of Pt complex (I-1), showing thereduced maximum EQE of only 1.53 at 5.5 V, maximum brightness of 12248cd/m² at a driving voltage of 16 V and with CIE coordinates of (0.58,0.42) at 8 V. Upon further increase of the dopant concentration to 100%,the device exhibited a much reduced EQE of 1.14 at 20 mA/cm², while themaximum brightness was lowered to only 4346 cd/m² at 16.0 V and CIEcoordinates was measured to be (0.62, 0.37) at 8 V. It is speculatedthat the lower efficiency at the higher dopant concentration could bedue to a combination of two factors, namely the longer emission lifetimeof τ_(obs)=8.2 ms and an increasing degree of aggregation despite itspossession of a bulky indazolate fragment. The net results may cause theinferiority of the doped devices mainly associated with triplet-tripletannihilation.

TABLE 2 Max lum. Quantum eff. Luminous eff. Power eff. conc. (%) [cd m⁻²(V)]^([a]) [%]^([b]) [cd A⁻¹]^([b]) [lm W⁻¹]^([b]) λ_(max)(C.I.E.)^([c]) 6% 20296 (16.0)  4.93 (3.16) 12.19 (7.82)  6.12 (2.96)581, 612 (0.57, 0.43) 12% 12248 (16.0)  1.52 (1.30) 3.64 (3.11) 2.03(1.27) 584, 614 (0.58, 0.42) 24% 9082 (16.0) 1.59 (1.29) 3.17 (2.58)1.71 (0.97) 596, 616 (0.60, 0.40) 50% 6425 (16.0) 1.19 (0.95) 2.14(1.71) 1.10 (0.61) 611 (0.61, 0.38) 100% 4346 (16.0) 1.14 (0.86) 1.70(1.29) 0.99 (0.52) 618 (0.62, 0.37) ^([a])values in the parentheses arethe applied driving voltage. ^([b])data collected under 20 mA cm⁻²,while values in the parentheses are the data collected under 100 mAcm⁻². ^([c])measured at the driving voltage of 8 V.

DEVICE EXAMPLE 2

The OLED of the present example was prepared in a similar procedure tothat described in Device Example 1 except that Complex (I-2) was usedinstead of Complex (I-1). The OLED of the present example emits orangelight.

DEVICE EXAMPLE 3

The OLED of the present example was prepared in a similar procedure tothat described in Device Example 1 except that Complex (I-3) was usedinstead of Complex (I-1). The OLED of the present example emits bluelight.

DEVICE EXAMPLE 4

The OLED of the present example was prepared in a similar procedure tothat described in Device Example 1 except that Complex (I-4) was usedinstead of Complex (I-1). The OLED of the present example emits bluelight.

DEVICE EXAMPLE 5

The OLED of the present example was prepared in a similar procedure tothat described in Device Example 1 except that Complex (I-5) was usedinstead of Complex (I-1). The OLED of the present example emits bluelight.

DEVICE EXAMPLE 6

The OLED of the present example was prepared in a similar procedure tothat described in Device Example 1 except that Complex (I-6) was usedinstead of Complex (I-1). The OLED of the present example emits bluelight.

Although the present invention has been explained in relation to itspreferred embodiment, it is to be understood that many other possiblemodifications and variations can be made without departing from thespirit and scope of the invention as hereinafter claimed.

1. A platinum complex of the following formula (I):

wherein X is a counter ion; n is 0 or 1; X¹ and X² independently are Cor N; R¹, R² and R³ independently are H, C1-C8 alkyl, phenyl, or C1-C4perfluoroalkyl, R¹ is H and R² and R³ together are

or R³ is H and R¹ and R² together are

when X¹ is C; R¹ and R³ independently are H, C1-C8 alkyl, phenyl, orC1-C4 perfluoroalkyl, and R² is omitted, when X¹ is N; R⁴ is H and R⁵ isH, C1-C8 alkyl, phenyl, or C1-C4 perfluoroalkyl, or R⁴ and R⁵ togetherare C4-C8 alkylene or bridged carbocyclic C4-C12 alkylene, when X² is C;R⁴ is omitted and R⁵ is H, C1-C8 alkyl, phenyl, or C1-C4 perfluoroalkyl,when X² is N; and L¹ and L² each are

when n is 1, or together are

when n is 0, wherein X³ is C or N; R⁶ and R⁷ independently are H, C1-C8alkyl, phenyl, or C1-C4 perfluoroalkyl; R⁸ is H, C1-C8 alkyl, phenyl, orC1-C4 perfluoroalkyl; X⁴ and X⁵ independently are C or N; each R′independently is H, C1-C8 alkyl, phenyl, or C1-C4 perfluoroalkyl; X⁶ andX⁷ independently are C or N; R⁹ is H and R¹⁰ is H, C1-C8 alkyl, phenyl,or C1-C4 perfluoroalkyl, or R⁹ and R¹⁰ together are C4-C8 alkylene orbridged carbocyclic C4-C12 alkylene, when X⁶ is C; R⁹ is omitted and R¹⁰is H, C1-C8 alkyl, phenyl, or C1-C4 perfluoroalkyl, when X⁶ is N; R¹¹,R¹² and R¹³ independently are H, C1-C8 alkyl, phenyl, or C1-C4perfluoroalkyl, R¹¹ is H and R¹² and R¹³ together are

or R¹³ is H and R¹¹ and R¹² together are

when X⁷ is C; and R¹¹ and R¹³ independently are H, C1-C8 alkyl, phenyl,or C1-C4 perfluoroalkyl and R¹² is omitted, when X⁷ is N.
 2. Theplatinum complex as claimed in claim 1, wherein X¹, X², X³, X⁴, X⁵,X⁶and X⁷ each are H.
 3. The platinum complex as claimed in claim 1,wherein R⁴ is H and R⁵ is H, C1-C8 alkyl, phenyl, or C1-C4perfluoroalkyl, or R⁴ and R⁵ together are

and R¹⁴, R¹⁵, and R¹⁶ independently are C1-8 alkyl.
 4. The platinumcomplex as claimed in claim 3, wherein R¹⁴, R¹⁵, and R¹⁶ each aremethyl.
 5. The platinum complex as claimed in claim 1, wherein R¹, R²and R³ independently are H, C1-C8 alkyl, phenyl, or C1-C4perfluoroalkyl; R⁴ is H; and R⁵ is H, C1-C8 alkyl, phenyl, or C1-C4perfluoroalkyl.
 6. The platinum complex as claimed in claim 5, whereinR⁵ is C1-C4 perfluoroalkyl.
 7. The platinum complex as claimed in claim6, wherein R⁵ is CF₃.
 8. The platinum complex as claimed in claim 1,wherein R¹ is H and R² and R³ together are

or R³ is H and R¹ and R² together are

R⁴ and R⁵ together are

and R¹⁴, R¹⁵, and R¹⁶ independently are C1-8 alkyl.
 9. The platinumcomplex as claimed in claim 1, wherein R⁹ is H and R¹⁰ is H, C1-C8alkyl, phenyl, or C1-C4 perfluoroalkyl, or R⁹ and R¹⁰ together are

and R¹⁴, R¹⁵, and R¹⁶ independently are C1-8 alkyl.
 10. The platinumcomplex as claimed in claim 9, wherein R¹⁴, R¹⁵, and R¹⁶ each aremethyl.
 11. The platinum complex as claimed in claim 1, wherein R¹¹, R¹²and R¹³ independently are H, C1-C8 alkyl, phenyl, or C1-C4perfluoroalkyl; R⁹ is H; and R¹⁰ is H, C1-C8 alkyl, phenyl, or C1-C4perfluoroalkyl.
 12. The platinum complex as claimed in claim 11, whereinR¹⁰ is C1-C4 perfluoroalkyl.
 13. The platinum complex as claimed inclaim 12, wherein R¹⁰ is CF₃.
 14. The platinum complex as claimed inclaim 1, wherein R¹¹ is H and R¹² and R¹³ together are

or R¹³ is H and R¹¹ and R¹² together are

R⁹ and R¹⁰ together are

and R¹⁴, R¹⁵, and R¹⁶ independently are C1-8 alkyl.
 15. The platinumcomplex as claimed in claim 1, wherein X¹, X², X³, X⁴, X⁵, X⁶ and X⁷each are C; R¹, R² and R³ independently are H or C1-8 alkyl, R¹ is H andR² and R³ together are

or R³ is H and R¹ and R² together are

R⁴ is H and R⁵ is C1-C4 perfluoroalkyl, or R⁴ and R⁵ together are

R⁶ and R⁷ each are H or C1-C8 alkyl; R⁸ is H or C1-8 alkyl; each R′independently is H or C1-C8 alkyl; R⁹ is H and R¹⁰ is C1-C4perfluoroalkyl, or R⁹ and R¹⁰ together are

R¹¹, R¹² and R¹³ independently are H or C1-8 alkyl, R¹¹is H and R¹² andR¹³ together are

or R¹³ is H and R¹¹ and R¹² together are

and R¹⁴, R¹⁵, and R¹⁶ are C1-8 alkyl.
 16. The platinum complex asclaimed in claim 1, wherein the platinum complex is


17. An organic light-emitting device, comprising: an anode; a cathode;and one or more organic medium layers including a light-emitting layerdisposed between the anode and the cathode, wherein at least one layerof the organic medium layers comprises a platinum complex of thefollowing formula (I):

wherein X is a counter ion; n is 0 or 1; X¹ and X² independently are Cor N; R¹, R² and R³ independently are H, C1-C8 alkyl, phenyl, or C1-C4perfluoroalkyl, R¹ is H and R² and R³ together are

or R³ is H and R¹ and R² together are

when X¹ is C; R¹ and R³ independently are H, C1-C8 alkyl, phenyl, orC1-C4 perfluoroalkyl and R² is omitted, when X¹ is N; R⁴ is H and R⁵ isH, C1-C8 alkyl, phenyl, or C1-C4 perfluoroalkyl, or R⁴ and R⁵ togetherare C4-C8 alkylene or bridged carbocyclic C4-C12 alkylene, when X² is C;R⁴ is omitted and R⁵ is H, C1-C8 alkyl, phenyl, or C1-C4 perfluoroalkyl,when X² is N; and L1 and L2 each are

when n is 1, or together are

when n is 0, wherein X³ is C or N; R⁶ and R⁷ independently are H, C1-C8alkyl, phenyl, or C1-C4 perfluoroalkyl; R⁸ is H, C1-C8 alkyl, phenyl, orC1-C4 perfluoroalkyl; X⁴ and X⁵ independently are C or N; each R′independently is H, C1-C8 alkyl, phenyl, or C1-C4 perfluoroalkyl; X⁶ andX⁷ independently are C or N; R⁹ is H and R¹⁰ is H, C1-C8 alkyl, phenyl,or C1-C4 perfluoroalkyl, or R⁹ and R¹⁰ together are C4-C8 alkylene orbridged carbocyclic C4-C12 alkylene, when X⁶ is C; R⁹ is omitted and R¹⁰is H, C1-C8 alkyl, phenyl, or C1-C4 perfluoroalkyl, when X⁶ is N; R¹¹,R¹² and R¹³ independently are H, C1-C8 alkyl, phenyl, or C1-C4perfluoroalkyl, R¹¹ is H and R¹² and R¹³ together are

or R¹³ is H and R¹¹ and R¹² together are

when X⁷ is C; and R¹¹ and R¹³ independently are H, C1-C8 alkyl, phenyl,or C1-C4 perfluoroalkyl and R¹² is omitted, when X⁷ is N.
 18. Theorganic light-emitting device as claimed in claim 17, wherein thelight-emitting layer is made of at least one host material doped withthe platinum complex.
 19. The platinum complex as claimed in claim 17,wherein X¹, X², X³, X⁴, X⁵, X⁶ and X⁷ each are H.
 20. The platinumcomplex as claimed in claim 17, wherein R¹, R² and R³ independently areH, C1-C8 alkyl, phenyl, or C1-C4 perfluoroalkyl; R⁴ is H; and R⁵ is H,C1-C8 alkyl, phenyl, or C1-C4 perfluoroalkyl.
 21. The platinum complexas claimed in claim 17, wherein R¹ is H and R² and R³ together are

or R³ is H and R¹ and R² together are

and R⁴ and R⁵ together are

and R¹⁴, R¹⁵, and R¹⁶ independently are C1-8 alkyl.
 22. The platinumcomplex as claimed in claim 17, wherein R¹¹, R¹² and R¹³ independentlyare H, C1-C8 alkyl, phenyl, or C1-C4 perfluoroalkyl; R⁹ is H; and R¹⁰ isH, C1-C8 alkyl, phenyl, or C1-C4 perfluoroalkyl.
 23. The platinumcomplex as claimed in claim 17, wherein R¹¹ is H and R¹² and R¹³together are

or R¹³ is H and R¹¹ and R¹² together are

and R⁹ and R¹⁰ together are

and R¹⁴, R¹⁵, and R¹⁶ independently are C1-8 alkyl.
 24. The platinumcomplex as claimed in claim 17, wherein X¹, X², X³, X⁴, X⁵, X⁶ and X⁷each are C; R¹, R² and R³ independently are H or C1-8 alkyl, R¹ is H andR² and R³ together are

or R³ is H and R¹ and R² together are

R⁴ is H and R⁵ is C1-C4 perfluoroalkyl, or R⁴ and R⁵ together are

R⁶ and R⁷ each are H or C1-C8 alkyl; R⁸ is H or C1-8 alkyl; each R′independently is H or C1-C8 alkyl; R⁹ is H and R¹⁰ is C1-C4perfluoroalkyl, or R⁹ and R¹⁰ together are

R¹¹, R¹² and R¹³ independently are H or C1-8 alkyl, R¹¹ is H and R¹² andR¹³ together are

or R¹³ is H and R¹¹ and R¹² together are

and R¹⁴, R¹⁵, and R¹⁶ are C1-8 alkyl.
 25. The organic light-emittingdevice as claimed in claim 17, wherein the platinum complex is